. The goal of this project is to define the proportion and characteristics of persons who should be vaccinated to control epidemic influenza. The Specific Aims are to demonstrate that immunization of school-age and preschool children will reduce illness in vaccinated children and unvaccinated contacts in the same age cohort, in addition to household and community contacts, regardless of immunization status. Influenza epidemic periods will be defined by virologic surveillance. Medically attended illness rates will be compared for two defined populations, one with vaccinated school children and the other without. County-wide surveys will be performed to determine whether significant reductions of hospitalization rates for acute respiratory conditions accompany the vaccine program. Evaluation will include the level of acceptance of immunization with an intranasally administered vaccine, the accessibility of the target population, the time required for administration of the vaccine and the cost effect.